1. Field of the Invention
The invention relates to processes for treating disc-shaped articles such as semiconductor wafers and glass wafers, and especially to processes for cleaning surfaces of semiconductor wafers.
2. Description of Related Art
Semiconductor wafers undergo a variety of wet processing stages during manufacture of integrated circuits, such as removal of photoresist from the wafer. When the photoresist is stripped by a wet process, typically a strong inorganic acid is used at high concentration, with sulfuric acid being most prevalent. Among the chemical compositions used for that stripping are solutions of sulfuric acid mixed with hydrogen peroxide (SPM) and mixtures of ozone and sulfuric acid (SOM). Also mixtures of sulfuric acid with hydrogen peroxide and ozone (SPOM) are being sometimes used.
The cleaning solution or mixture including a high concentration of strong inorganic acid must then itself be removed from the wafer surface. However, highly concentrated inorganic acids, and especially sulfuric acid, are highly viscous, and it therefore requires an extended period of rinsing to remove the acid-based cleaning liquid from the wafer surface.
For example, removal of the sulfuric acid after a convenional photoresist strip process in a process module for single wafer wet processing typically requires a minimum of 150 seconds when deionized water (DI) followed by an SC-1 mixture (NH4OH/H2O2/H2O) is being used, with the necessary time being approximately twice as long as that when only deionized water (DI) is used to rinse away the acid. A shorter rinsing time leads to a time dependent crystal formation on the substrate surface.
In addition, when using an SC-1 mixture significant equipment problems arise due to crystal formation in the exhaust and drain lines, those crystals being the product of ammonia vapor reacting with sulfate residues to form for example ammonium sulfate and ammonium bisulfate. This protracted removal step also leads to higher cost of ownership and lower throughput due to higher chemical consumption and long process times.
Similarly, semiconductor processing already consumes substantial volumes of deionized ultrapure water (UPW), which can have a negative environmental impact, especially given that the current generation of 300 mm wafer has more than twice the surface area of the previous 200 mm wafer. Soon 450 mm wafer might become the next new standard for semiconductor processing, which will necessitate still further measures to reduce the usage of ultra pure water (UPW). Techniques that limit consumption of ultrapure water during processing of semiconductor wafers will therefore yield multiple benefits.